1. Field of the Invention
The invention relates to freezing liquid in a conduit, and more particularly to a method and device for producing a freeze seal by the use of cryogenic gas.
2. Description of the Prior Art
As indicated in U.S. Pat. No. 3,041,850 to Nunn, a known procedure for stopping the flow of water in a pipe line is to freeze water in the line to form a plug. The Nunn patent describes the prior use of solid carbon dioxide, "Dry Ice" to accomplish freezing, and asserts that the use of carbon dioxide gas supplied from a pressure tank to an expansion chamber arranged around a pipe is preferable to the use of a refrigerant in solid form.
Tremont U.S. Pat. Nos. 3,498,071 and 3,623,337 mention the use of liquified air and inert gases such as kypton, argon, neon and nitrogen to freeze liquid in a pipe section and describe a layered pipe jacket in which the liquid refrigerant expands to the gaseous state to effect freezing.
U.S. Pat. No. 3,695,301 to Pittman describes a freeze sealing technique using a body positioned within the pipe as well as an external refrigerant tank containing solid carbon dioxide.
Grise U.S. Pat. No. 3,742,723 relates to a pipe freezing device by causing freezing gas to flow through an annular chamber clamped around the pipe. The chamber can be formed of a split hollow ring, or two hingedly interconnected hollow half rings.
An article in the periodical Electrical World dated Jan. 1, 1975, pages 38-40 entitled "Plug technology adapted for reactor repair" describes the use of liquid refrigerant to form freeze seals at a nuclear power generating station.
The use of freeze seals for large pipes is described in the periodical Pipe Line Industry, March 1977, pages 37-39 in an article entitled "Quick freeze plug reduces testing and repair costs". Liquid nitrogen is said to have proven to be the most effective freezing agent.
The hazards of handling liquid nitrogen are well known, but it appears that prior art techniques have employed liquid nitrogen to take advantage of the fast cooling effect when the nitrogen "flashes" to the gaseous state. However, this flashing does not allow controlled even cooling down of pipes and their contents. Sudden cooling can impose great stresses on pipe wall materials, and the thermal shock caused by exposing a pipe directly to extremely cold boiling nitrogen can damage the pipe wall structure. A rapidly expanding ice plug within the confines of a pipe can exert extreme outward force against the pipe wall. These problems have not been fully solved by the prior art.